Telegraph signal distortion indicating and measuring device



Feb. 2, 1954 s. l. oRY TELEGRAPH SIGNAL DISTORTION INDICATING AND MASURING DEVICE 4 Sheets-Sheet 1 Filed April 2, 1952 /NVENTOR CO/Py By@ um wemw -bnf E v w S,

n. w s u?. .o @Dx ATTO NE'V S. l. CORY Feb. 2, 1954 Filed April 2, 1952 4 Sheets-Sheet 2 /Nf/EA/TOR S. I. CORV BV ATTORNEY 4 Sheets-Sheet 5 Feb. 2, 1954 s. l. coRY TELEGRAPH SIGNAL DISTORTION INDICATING AND MEASURING DEVICE Filed April 2, 1952 Feb. 2, 1954 TELEGRAPH SIGNAL DISTORTION INDICATING AND MEASURING DEVICE Filed April 2, 1952 PERFECT .f/GNL OUTPUT VOLTAGE OF TUBE V/ OUTPUT VOL TAGE OF TUBE V2 0.U TPU T VOLTA G E OF TUBE VJ OUTPUT VOLTAGE 0F TUBE V4 D/FFERE/VT/ATED O U TPU T VOLTAGE OF TUBE V/ P/P I aus l S. l. CORY 4 Sheets-Sheet -4 SPACEIJPACE MARK SPACEISPACEISPCE MARI( ATT RNEV Patented Feb. 2, Y1954 TELEGRAPH SIGNAL DISTORTION INDICAT- ING AND MEASURING DEVICE Samuel I. Cory, Towaco, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 2, 1952, Serial No. 280,102

7 Claims.

This invention relates to telegraph testing equipment and more particularly to a portable testing set comprising, among its miniature parts, a miniature cathode-ray tube for indicating both the sign and amount of bias and end-distortion present and the peak value of the total distortion in telegraph signals.

It is an object of this invention to obtain a luminescent indication of both the sign and the amount of bias and end-distortion and the peak value of the total distortion present in signals 0I" the live or six unit permutation code type transmitted over a system without disturbing the transmission of the signals over such system.

It is also an object of the invention to obtain an indication of the sign and the instantaneous values of bias and end-distortion, and the peak value of the total distortion present in signals on start-stop printing telegraph circuits, the indication being in the form of momentary flashes of light or a spot of light appearing in one direction only along the sweep of the electron beam at the horizontal axis on the screen, or face, of a lcathode-ray tube.

Another object is to produce ilashes of lighti.v

y type of distortion present in the signals, the

flashes appearing above the axis to indicate bias and below the axis to indicate end-distortion. A persisting indication of peak value of total distortion is afforded by the position of a spot of light along the axis.

Another object is to adapt the device of the present invention for use with both the five and six unit teletypewriter character signal code at any chosen speed of transmission.

In an embodiment of the present invention the device for indicating the signal distortion is of the portable type primarily for use at customers stations but it may be used on a permanent basis at the testboard positions in central oces. The

device, or set, is all electronic-in that no electromagnetic relays are employed and comprises a one-inch cathode-ray tube, miniature vacuum tubes and germanium rectiers in circuits which operate on a voltage basis rather than on a current basis. This keeps the power requirements small. so that only a small self-contained power supply is needed. The set has its own ground, that is, its own voltage reference point, which is not to be confused with the physical or external ground of the subscribers station or the oiiice wherein the set is employed. rIhe essential parts of the set are an input trigger-tube circuit, a oneshot multivibrator character timer, a multivibrator pulse-timer, an integrating circuit, a horizontal sweep amplifier, diierentiating circuits, a peak-distortion indicating circuit, a meter circuit for recording peak-distortion with automatic resetting means and a one-inch cathode-ray tube with a 21/2 power optical magniiier.

A feature of the invention is the provision of means for making a local check that is simple and quick without requiring a local source of test signals.

Another feature is the provision of means responsive to signaling pulses for producing along the sweep of the cathode-ray beam at the horizontal axis on the face of the cathode-ray tube momentary upward deflections of the beam, called pips, to indicate the amount of bias. The gradually receding tails of these pips are in one direction for marking bias and in the opposite direction for spacing bias.

Another feature is the provision of means re- Sponsive to signaling pulses for producing along the electron beam sweep at the horizontal axis on the face of a cathode-ray tube momentary downward deections of the beam, also called pips, to indicate the amount of end-distortion. The gradually receding tails of these pips are in one direction for marking end-distortion and in the opposite direction for spacing end-distortion.

Another feature is the provision of means responsive to signaling pulses for producing along the electron beam sweep a spot of light, the position of which indicates the maximum amount of the total distortion, or the peak-distortion, present in the signals.

Another feature is the provision of means for obtaining a continuous indication of peak-distortion present in the signals. A resetting circuit automatically operated is incorporated to restore the distortion indication to zero periodically whereby more information is obtained regarding the distortion variations than would be obtained by allowing the meter indication to drift back slowly at a rate determined by leakage across a peak-voltage storage condenser.

Another feature is the provision of static adjustmcnt means used in conjunction with a bias potentiometer in the signal input circuit whereby the accuracy of the bias adjustment is improved, especially, when the set is operated with rounded wave shaped signals as are usually received at the termination of a subscribers loop circuit. These means provide a static method, that is, a steady marking current flows through the input of the set, during adjustment of the potentiometer.

The above 'and other objects and features of the invention are set forth in the following description and appended claims, and may be more readily understood and considered in conjunction with the accompanying drawings of which:

Figs. l and 2 show the schematic layout of the electronic distortion indicating set;

Fig. 3 shows a self-powered circuit including a cathode-follower type of electronic tube for operating .a recording meten and 'an *adjustable .reset device'for automatically restoring the'meter to normal at regularly recurring intervals of predetermined duration; A

Fig. 4 is a series of charts showing thepip indications of bias and end-distortion `and .the spot indication of maximum peak-distortion obtained by means of the circuit shown `in'ligs'. land .2;

Fig. 5 shows a chart containing a :series of traces of operating wave shapes for variousparts of the circuit of Figs. 1 andfz; and

Fig. 6 shows the relative arrangement of Figs. 1, 2 and 3.

The set described herein is provided with a pip-peakA switch 6.6 having six bladesii-I to 66-6 and two positionsV into which it may be operated. In one position pips of light are produced on the electron beam sweep along the horizontal axis on the face of the cathode-ray tube'to indicate the sign and amount oi bias and end-distortion and in the other a spot of light is produced on 'the electron-beam sweep ,to indicate the amount of peak-distortion. Itis provided also with speed switch A52 having four blades 52-I to 52-4 -whichare arranged to be *positioned for three different speeds of transmission, namely 60 or '75 or 100 speed service.

The input trigger-tube circuit vof Fig. `1 performs the same functionfas an electromagnetic receiving relay. Twin-triode vacuum tube VI Aforms part of the input trigger-tube circuit. :The leftand right-hand triodes of vacuum tube VI are designated NC. and C., respectively, to indicate their normal conditions, that is, nonconducting and conducting. Theinput triggertube circuit is arranged toreceive neutral signals of any current value between .015 and. .080 ampere, polar signals, or ,electronic hubcircuit signals without disturbing the service.

The character timer comprises twin-triode vacuum tube V2 .which is a single shot multivibrator. The leftand right-hand triodes are designated NC. and C., respectively, `to lindicate their normal conditions, that upon-conducting and conducting. In response to the start pulse, or element, of a .start-stop telegraph signal which in this case is a pulse of positive potential, the .left-hand triode becomes conducting and the right-hand triode becomes non-conducting inasmuch as the polarity has become reversed by vacuum tube VI. The circuits of these triodes are so arranged that the Vtriodes remain in such operated condition until the stop element of the .signal is received.

YThe pulse-timer is a local source or pulse timving with which the pulse timing of an incoming signal is compared to indicate signal distortion. It uses vtwin-triode .vacuum tube V3 as afree running multivibrator which produces a squared- ,.NC., respectively, to indicate ,their conducting ,and non-.conducting normal conditions.

The output of the pulse-timer is ,impressed on an integrating circuit comprising sweep amplitude potentiometer I I, resistor I2 and any one of condensers I3, I4 and I5 having a suitable value for each of the transmission-speeds of 60, '75 and Atimer into a triangular-shaped .vv/ave.

4 speed teletypewriter service, for converting the squared-topped output wave of lthe pulse- The triangular-shaped wave is suitably amplified by imeans of the left-hand triode of vacuum tube Vlland the right-hand triode of each of vacuum tubes V5 and V6, in vseries connection, the righthand triodes of tubes V5 and V6 being of the cathode-follower type. The amplified triangular- 'shaped wave'is applied to horizontal plate No. 6 vofrcathode-raytube I6 to cause the electron beam to sweep `to and fro along the horizontal axis of the Yface ofthe 'cathode-ray tube I6. The horizontalsweep is adjusted to extend the full length of the 0 to 50 per cent distortion scale along the entire horizontal axis of the face of cathode-ray tube I6.

Connected to the output circuit of right-hand triode of tube VI are two differentiating circuits. One of these comprises condenser I1 and is connected to vertical deiiection plate No. 4 of the cathode-ray tube I6 to produce pips along the .horizontal sweep on the face of cathode-ray tube I6 at the times of occurrence of transitions in .the incoming signal. These pips and the positions at which they appear along thehorizontal sweep of tube I6 indicate the amount, type and sign of distortion present lin the signal. The second differentiating circuit comprises germanium diodes .2 and 2i and .associated resistors and condensers. It produces rectified sharp Ipulses of short duration at the times of occurrence of transitions. These are amplified by the left-hand triode of vacuum tube V5 and then applied to Ygrid No. 5 of the cathode-ray tube I6 in such a -directionas to intensify the pip indication of distortion. This circuit is lalso used in providing the peak indication of distortion as is hereinafter described. Diodes 2i) and 2l are of ,the P-N junction type shown in J. H. Scaff- .I-I. C. Theuerer Patent 2,602,211, granted July 8, 1952. lThis type of rectier is noted for its highba'ck resistance, high 'forward conductance, `low powerrequirements, very low capacity effect,

and small size.

To indicate peak-distortion the pip-peak" Vswitch 66 'is operated to its No. 2 position. The

triangular-shaped sweep voltage appearing on the plate No. 6 of vacuum tube V4 as hereinbefore stated, is sampled at'the times of occurrence of 'transitions and these voltage samples are stored on'condenser I8 to control the'position Jof the spot of light along the horizontal axis of cathode-ray tube I6. Sampling is accomplished by using the right-handtriode of tube V4'as'a 'gate'triode 'This triode is normally conducting. -Rectied sharp pulses obtained from the :second diierentiating circuit hereinbefore described, areamplied and applied tothe grid `to charge condenser I8 in the cathode circuit of the left-hand triode of tube V6. The lefthand triode of tube V6 is used as a rectier to prevent the charge on condenser I8 from leaking back to ground throughresistor 32. Con- -.denser Iis connected to the grid of the righthand triode of tube V6 and the output of this right-hand triode, which is, as hereinbefore stated, of the cathode follower type, is applied directly to the horizontal deflection plate No. 6 of cathode-ray tube iii to cause the cathoderay beam, indicated as a spot of light, to move to a position along the horizontal axis of tube I6 corresponding to the per cent of peak-distortion in the incoming signals. The high resistance of resistor I8 which is of a resistance value, say of 500 megohms, the incidental leakage in the condenser I8 and the left-hand triode of tube V cause the voltage on condenser I8 to leak oli slowly and cause the position of the beam along the horizontal axis of tube I6 t0 drift back slowly to zero. Should the spot of light stay at the zero end oi the axis there would be no distortion present in the signal but should it appear at any other point along the axis the spot would indicate the per cent of peak-distortion present. This persisting type of peakdistortion indication on cathode-ray tube l5 serves the same purpose as the similar indication obtained by the peak-distortion indicating meter of the sets respectively described in F. A. Cowan Patent 2,132,278, granted October 1l, 1938, and Rea-Wilkerson Patent 2,370,685, granted March 6, 1945.

The power-supply circuit for the set is a conventional rectiiier circuit using selenium recti- 'lers 23 and 2li for the positive high voltage, say, of about 265 volts and selenium rectifier for the negative high voltage, say, of about 2745 volts. A source of alternating current of 60 cycles and 115 volts, such as source '20, furnishes power to transformer 2l. Transformer 27 furnishes the above-mentioned positive and negative high voltages and the filament current for tubes Vi to V5 inclusive. A separate transformer 28 furnishes from the same source 20 filament current for tube V5.

DETAILED DESCRIPTION Input circuit The telegraph transmission measuring set of the present invention has two jacks 2a and 30, jack 29 being provided for connecting to a line or a trunk circuit on which neutral or polar signals are employed and jack 30 for connecting to an electronic hub circuit using a positive potential of 60 volts for marking and a negative potential of 30 volts for spacing. Both jacks are connected to the input trigger-tube circuit. When jack 29 is used resistor 3l having a resistance value, say ci 75 ohms, which is in the cathode circuit of both triodes of tube Vl, is inserted in series in the telegraph line or trunk circuit under test. When jack 30 is used resistor` 32 having a resistance value, say of 0.82 megohm, is in series between the hub circuit under test and the input circuit to the measuring set. Because of the low input impedance of the measuring set circuit when used with a line or a trunk circuit, and the high input impedance when used with a hub circuit, there. is practically no effect on the circuit under test due to the connection of the set to the circuit in either case. Potentiometer 33 comprising resistors 35i and 35 which have resistance values of say 2.0 and 0.1 megohms, respectively, is referred to herein as a bias potentiometer. It is connected to the positive output of the powersupply circuit. In order to adjust the bias potentiometer for incoming polar signals, switch I-CP is operated to its closed position and the proper adjustment of potentiometer 33 is then made, but

when the incoming signals are of the neutral type switch I-CN is operated to its closed position wherein resistor l-CN having a resistance value equal to that of resistor 3|, in this case, 75 ohms, is included in the cathode circuits of tube VI and the proper adjustment of potentiometer 33 is then made. When potentiometer 33, which furnishes a variable bias for the grid of the left-hand triode of tube VI, is properly adjusted the input trigger-tube circuit has two stable conditions and responds to incoming signals of the start-stop type in much the same manner as an electromagnetic relay. The input trigger-tube circuit in its normal condition, that is, with marking current on the line circuit under test, finds the left-hand triode of tube Vl non-conducting and the right-hand triode conducting. Whereas, when a space signal is on such circuit the left-hand triode becomes conducting and the right-hand triode becomes nonconducting.

It is assumed that the input trigger-tube circuit is connected to a closed telegraph line circuit having a current of 0.062 ampere. The right-hand triode of tube Vl is then conducting and the left-hand triode is not conducting. The voltage drop across resistor 3| due to the ow of current over the line circuit connected to jack 29 is in such a direction as to cause a small negative bias on the grid of the left-hand triode of tube VI. This negative bias added to a negative bias resulting from the flow of plate current from the normally conducting right-hand triode of tube VI, through cathode resistor 31 having a resistance value, say of 1800 ohms, and the positive bias provided by potentiometer 33, causes the grid of the left-hand triode of tube VI to become negative with respect to its associated cathode and therefore holds the left-hand triode in a non-conducting condition. When the lefthand triode of tube VI is non-conducting, the plate ofthe left-hand triode has a high positive potential, the potential being furnished by a xed potentiometer comprising resistors 38, 39, and 40 having resistance values, say of 0.22, 0.56 and 2.0 megohms respectively. The xed potentiometer connected to the plate of the left-hand triode of tube V i is also connected to the grid of the right-hand triode and causes the right-hand triode to be conducting when the left-hand triode is non-conducting.

The spacing condition on the line circuit resulting from the start element of a telegraph start-stop signal received at jack 29, shown in trace A in Fig. 5, causes the eiective bias on the grid of the left-hand triode of tube Vl to become positive with the result that the left-hand triode becomes conducting. When the left-hand triode conducts, potential on the plate of the lefthand triode decreases and is no longer eiective to hold the grid of the right-hand triode positive. The grid of the right-hand triode becomes negative to cause the right-hand triode to become at this time non-conducting.

The output voltage from the plate of the righthand triode of tube VI is about 25 volts when the right-hand triode is conducting as for a marking element of the signal and about 235 volts positive when the right-hand triode is cut oir as for a spacing element. The change from high to low potential is very rapid due to the feedback action through the common cathode resistor 31, as is indicated in trace B of Fig. 5.

Potentiometer 33 has sufficient range to permit satisfactory adjustment for the reception of ,uve-.unit i code character signal. Vlitive'-fvcltage .ontheplateof 1the right-.hand triode enculee .neutral .or .polar signals of the usual current values. .Theoutputcf tube Vl iis used directly to.controlthecharacter timer circuit comprising rtube V2 and is also applied to the diierentiating circuits-to furnish indications of the times of occurrence oftransitions in the incoming signals as is explained below.

Character-timer circuit The character-timer circuit is, as heretofore stated,.a. one-shot multivibrator employing twintriode tube V2, the tube being controlled by the .output oftube V l through resistor 4l having a ,resistance value, say of 6.2 megohms. If it is assumed that a stop pulse which is marking, is .being received, theplate of the right-hand triode .of ,tube Vl and the plate o1" the right-hand triode .of `tube V2 Willhave lowpositive voltages. The .low .positive voltage from the plate of the righthand triode of tube V l is applied to the grid of the left-hand triode of tube V2 through resistor AAl,.and is not .effective to overcome the negative Vvoltagesupplied from the fixed ,potentiometer .comprisingresistors 42, 43 and de having re- V.sistance values, sayof r?5,000 ohms, 0.68 megohm and 1.8 megohms, respectively, with the result -thatthe left-hand triode of tube V2 remains non- ;conducting. vwhen the right-hand triode of tube Vi `becomes .non-conducting in response to the lstart element of an incoming signal, the grid of vthe leftehandtriode of tube V2 becomes positive -withrespect .to .its cathode and the left-hand `.triode of ,tube`V2..beeomes conducting thereby reducing thepositive potential on the .plate ofthe :left-.hand triodeof tube V2. The decrease in V.potential ofthe plate of the left-hand triode of .tube V2 .is applied to thegrid of the right-hand v.triode of A.tube V2, .through condenser A5 which hasa. capacitance value, .say of 0.025 microfarad, `andcauses. this gridto become negative with respect to its cathode and the right-hand triode .therefore becomes non-conducting to start a -timinginterval VDuring this timing interval the ,'gridof the right-hand triode of tube V2 remains .negative and .the .character-timer circuit does vnot-respond to the other transitionsin the in- -coming signal. About the time when the succeeding stop pulse at the end of the character is :received fthe character-timer circuit returns to its normal condition and remains in such condition until the start pulse of the next incoming :signal is received. Upon the receipt of the start .element of the succeeding incoming signal the 'condition of-the character-timer circuit is again "changedsuddenly causing a negative bias to be impressed on the grid of the right triode of tube V2 through timing condenser 45. Resistor 41 :is one of three resistorsarranged for engagement -'by blade..522 of the speed switch 52 wherein Vresistorlll is'selected for60 speed, resistor i8 for "7-5speed landresistor Ailv for 100 speed, resistors @Sand-49 having resistance values, say of 2 and 0.3 megohms, respectively. Condenser 45 when charging, charges slowly through timing resistors -fii,-ll(for .60fspeed) and resistors 50 and 5i ci the character potentiometer. Resistors 4S, 41, 50 -andsl .have resistance Values, say of 5.6, 3.8, 0.1:and 0.75 megohms.

4Because of the slowly changing charge on con- `denser i5 .thegrid on the vright-hand triode of tube V2 doesnot become sufficiently positive to permit conduction .until approximately the end ci the sixth pulse of an incoming signal of a The loW pos- .of tube V2 at this time -assistsin stopping the pulse-timer circuit as shown in trace C oflig. 5

Pulse-timer circuit The pulse-timer circuit is a conventional multivibrator employing twin-triode tube V3. With each triode is the usual feedback circuit and a potentiometer. The potentiometer associated with the left-hand triode comprises resistors 55 and 5l and that associated with the right-hand triode comprises resistors andi-9. The former potentiometer applies a fixed positive voltage to the grid of .the left-hand triode voi tube V5 and the latter potentiometer due toits connection to the plate of the right-hand triode ci tube V 2 applies a negative or positive Voltage to the grid of the right-hand triode of tube V3 depending cn Whether the right-hand triode of tube V2 is conducting or non-conducting at the time. As hereinbefore stated, during the stop pulse, or element, or an incoming signal the right-hand triode or tube V3 is non-conducting. The resistance value cfresistors 54, 55, 55, 5l, 58 and 50, all of which form part of the xed potentiometer, have resistance values say of 0.1, 1.0, 0.68, 0.68, 0.68 and 0.58 megchms, respectively.

Upon the receiptof the start element of an incoming signal, that is,.at Vthe transition from marking to spacing, the character-timer circuit operation is startedand the voltage at .the plate of the right-hand triodeor tube V2 increases to a high positive value, as hereinbefore stated. Therefore, the potential of Vthe grid of the right hand triode of tube V3 becomes positive and of about the same positive value as that on the grid of the left-hand triode of tube V3 assuming that the multivibrator balance potentiometer 53 is properly adjusted. At the same time a negative voltage pulse is applied to the plate of the righthand triode of tube V3, through condenser 50 which has a capacitance Value, say of 0.0002 microfarad. Both of these actions cause the pulse-timer circuit to start promptly. It continues to oscillate freely until the following stop pulse, or element, of the signal arrives. The output is represented by the rectangular voltage- Wave shown at trace D in Fig. 5. Coarse speed adjustments of the pulse-timer circuit are made at one of variable potentiometers 5l, 62 or each of which has a maximum resistance value of 0.1 megohm. The selection of the proper potentiometer of potentiometers 5I, E2 and 53 depends upon the speed oi transmission on the line circuit under test and is determined by means of switch blades 52--3 and .52-4 of speed switch 52. The fine speed adjustment is made by means of the une potentiometer 64 which has a maximum resistance value of 20,000 ohms. Switch blade'52-4 is connected to the movable contact of line potentiometer 5.1i, through resistor 65 which has a resistance value, say of 47,000 ohms. When the speed is properly adjusted the pulse-timer circuit makes one complete cycle for each element length in an incoming signal, as shown at D, Fig. 5.

Integrating circuit The rectangular Voltage-Wave at the output of the pulse-timer circuit is converted into the triangular-shaped Wave as shown in trace E of Fig. 5 by means of-an integrating circuit comprising resistor I2 of a resistance value, say of 10 megohms, sweep amplitude potentiometer II having a maximum resistance value, say of megohms, and any one of condensers I3, I4 and I5 having capacitance values of 0.0231, 0.0185 'and 0.0142 microfarad, respectively, in cooperation with the input circuit of the left-hand triode of tube V4. The selection of the desired condenser of condensers I3, I4 and I5 is made by means of switch blade 52--I depending upon whether the speed of transmission on the line circuit under test is of 60, '75 or 100 speed. The integrating circuit has a large time constant. The voltage on the selected condenser reaches only a small fraction of the maximum potential on the plate of the right-hand triode of tube V3 in the time of a half-cycle oi the pulse-timer circuit. Accordingly, there is practically a linear change in voltage appearing on the condenser during each half-cycle of the pulse-timer circuit. This triangular wave is ampliiied by the lefthand triode of tube V4. When the pip-peak switch 66 is in its pip, or No. 1 position, the amplified wave is applied to horizontal deflection lplate No. 6 on cathode-ray tube I, through two cathode-follower triodes, that is, the right-hand triodes of tubes V5 and VS in tandem, thus causing the desired linear horizontal sweep voltage across the horizontal axis of cathode-ray tube i8. The amplitude of this sweep may be adjusted by means of the sweep amplitude potentiometer Il so that the luminous trace on the face of the cathode-ray tube I6 extends between the zero and the 50 per cent points (the entire length) on the distortion scale along the horizontal axis. The sweep-level potentiometer comprising resistors 5l" and 68 which have resistance Values, say of 1.0 and 0.1 megohms, respectively, permits adjusting the steady bias of the left-hand triode of tube V4 so that the output of the tube appears as a triangular wave of equal amplitude and constant level, that is, all the zero positions of the sweep are just touching the bright luminous spot formed by the electron beam when such beam is at rest at the zero end of the scale. The desired sweep voltage for a teletypewriter character signal is as shown at trace E in Fig. 5 obtained when the sweep level potentiometer and sweep amplitude potentiometer II are properly set. The proper adjustment of the sweep level potentiometer predetermines the bias applied to the grid of the left-hand triode of tube V4 to cause grid current to flow when the condenser of condensers I3, I i and I5 requires its maximum voltage, that is, when the beam is at its zero position as mentioned above. Adjustment of one of the sweep potentiometers aiTects the other and vice versa, so that it is necessary to adjust one and then the other to obtain the desired amplitude and level.

Diierentiating circuits One of these circuits extends from the connection at the mid-point 69 of resistors 10 and 1I, each of which has a resistance value, say of 51,000 ohms in the plate circuit of the rightvhand triode of tube VI,` over conductor 16, conalong the horizontal axis of tube I6. The change in voltage on the plate of the right-hand triode of tube VI for a space-to-mark (upward direction) transition causes an upward pip and for a mark-to-space (downward direction) transition causes a downward pip as shown in trace F in Fig. 5. The rapid voltage change in the potential of the plate of the right-hand triode of tube VI in response to a transition in an incoming signal causes the initial movement of the electron beam in cathode-ray tube I t to be rapid and therefore it is barely visible at the beginning of a pip but the subsequent relatively slow charging of condenser I'I in a logarithmic fashion through resistor 'I3 which has a resistance value, say of l megohm, appears as a bright trace which slopes to the left for marking bias and to the right for spacing bias as shown in trace A in Fig. 4, and to the right for making end distortion and to the left for spacing end distortion as shown in trace B in Fig. 4.

A second differentiating circuit comprises the connection 'I4 between resistors il and 75, the latter resistor having a resistance value, say of 0.12 megohm, in the plate circuit of the righthand triode of tube VI, and extends over conductor 12, resistor 22 having a resistance value, say of 82,000 ohms, condenser 'il having a capacitance, say of 0.01 microfarad, through a network comprising germanium diodes 20 and 2l. In this second differentiating circuit there is impressed a second portion, different from the rst, of the transient voltage of the output of tube Vi, on the diodes 20 and 2I to produce across resistors 04 and 85 having resistance values, say of 30,000 and 20,000 ohms, respectively, unidirectional pips corresponding to the transitions in the incoming signal. These pips are applied over switch blades Sii-3 and dt-fi of pip-peak switch 66 to the grid of the left-hand triode of tube V5 wherein they are amplied. When pippeak switch 66 is in its position No. 1, the amplified unidirectional pips are in a positive, or upward, direction and are impressed on the intensity grid No. 5 of cathode-ray tube I6 in a path extending over conductor 78, blade SiS-I of the pip-peak switch 66 in its No. 1 position, conductor 79, condenser 30 having a capacitance, say of 0.01 microfarad, resistor 8l having a resistance value, say of 10 megohms, and conductor 82 to the intensity grid No. 5 of the cathoderay tube I6. These amplified voltage pips serve to intensify the brightness of the pip indications appearing along the horizontal axis of tube I6. When pip-peak switch 66 is in its No. 2 position the amplied unidirectional pips are in a negative, or downward, direction and are impressed on the grid of the right-hand triode of tube V4 (a gating triode) to cause this triode to become momentarily non-conducting for the duration of each pip whereby momentary samples of the triangular-shaped sweep voltages available at the plate of the left-hand triode of tube V4 are successively applied to the grid of the right-hand triode of tube V5 to furnish peak-distortion voltages as will now be described in more detail.

Peak indicating circuits To obtain the persisting indication of peakdistortion on the face of cathode-ray tube I6, the triangular-shaped sweep voltage available at the plate of the left-hand triode of tube V4 is sampled at the time of the transitions of the incoming signals and these voltage samples are stored on condenser I8 which has a capacitance 11 value, say of 0.05 microiarad. Condenser I9 is connected in the cathode circuit of the left-hand triode of tube V6 when blade 56--6 of the pippeak switch 66 is in its No. 2 position.

The operation of the circuit is as follows: A -portion of the voltage output of tube VI is differentiated and rectied to obtain unidirectional pips all of which are of negative polarity because ,of pip-peak switch 66 being in its No. 2 position. The rectifier circuit comprises two parallel paths wherein germanium diodes 20 and 2| are respectively included. The unidirectional output of the rectiiier circuit is amplied by the lefthand triode of tube V with switch blades @ie- 3 .and 66--4 in their respective No. 2 positions. In

the output of the left-hand triode of tube V5, the unidirectional pips of negative polarity are of short duration and substantially uniform height, one pip for each transition in an incoming signal. These negative voltage pips are successively impressed on the grid of the right-hand triode of tube V4 so that the latter triode becomes non-conducting during the interval of each pip which is, of course, at the time of each transition in the received signal. While the right-hand triode of tube V4 is thus momentarily non-conducting, the instantaneous voltage of the triangular sweep which is present on the plate of the right-hand triode of tube V4 is applied to the grid of the right-hand triode of tube V9. The right-hand triode of tube V5 is or the cathodefollower type and the sampled sweep voltage present on its grid causes a charge to be stored on condenser |8 over a circuit extending through the left-hand triode of tube ve, switch blade Q 66-6 in its No.2 position, condenser E9 to ground. The grid and plate of the left-hand triode ci vacuum tube V6 are connected together so that this triode acts as a rectifier which allows the 0.05 Inicroarad condenser I8 to charge and then prevents the charge from leaking off through resistor 32 to ground. Condenser 8 is also connected to the grid of the right-hand triode or tube V6. The right-hand triode of tube V6 also is of the cathode-,follower type and the output directly to horizontal deof this triode is applied nection plate No. 6 of the cathode-ray tube i6. It will be noted that resistor |8 having a leak resistance value, say of 500 megohins, is connected across condenser I8 in the cathode circuit of the left-hand triode of tube V6 to cause condenser |8 to have a denite amount or leakage and hence to cause the spot oi light which serves to indicate the peak-distortion to have a definite but slow drift-back rate. Reset key 83 is associated condenser may be discharged at will in order to restore the indication to Zero.

Meter circuit for recording peck-distortion The peak-distortion may also be recorded on a graphic meter of the portable type such as manufactured by the Esterline-Angus Company of Indianapolis, Indiana. This type of recording with condenser i9 so that the provides a continuous record of peak-distortion A over long periods of time. The recording meter circuit is shown in Fig. 3 and is self-powered ior use on 110 volts, 60 cycles power. It comprises in addition to the graphic meter an amplier vacuum tube V1 of the cathode-follower type for operating the meter, and an adjustable automatically operated reset circuit which may be set to operate at deinite intervals, say or 0.5 to 10 seconds duration. The meter represented by block 86 is plugged into jack 89 for connection to tube V1.

The output of the right-hand triode of tube V6, which is applied directly to horizontal deiiection plate No. 6 of cathode-ray tube I6 for indicating the peak-distortion, is also applied over conductor 81 to the grid of tube V1 for operating the recording meter circuit. As a result of this output voltage, current flows in the circuit traceable from potentiometer 88, sleeve of jack 89, graphic meter 8S, tip of jack 89, conductor 90, resistor 9|, cathode and plate of tube V 1, conductors 92 and 93, to the connection point |04 of positive potential connected to the positive side of power transformer 94, whereby meter 6G records the amount of peak-distortion present in the signals incoming at the transmission measuring set. Tube V1 is made sensitive by means of adjustable resistor 9| so that indications made on meter` 86 are full scale to the right from the center zero to 50 per cent distortion in a manner corresponding to the peak-distortion indicated along the horizontal axis of the face of cathoderay tube I6 of the transmission measuring set. Deiiections of the meter needle to indicate various amounts of peak-distortion for use in checking the sensitivity setting may be produced by momentarily operating the speed switch 52 in the transmission measuring set to a speed other than that in use at the time and comparing the distortion indicated on tube I6 with that indicated by the recording meter.

The adjustable automatically operated reset circuit provides means for periodically restoring the peak-distortion indication to zero value so as to show on the recorder chart more information regarding the distortion variations than would be obtained by allowing the meter indication to drift back slowly at a rate determined by the leakage across peak-voltage storing condenser I8. In this automatically operated reset circuit is provided condenser-resistance timing by means of condenser and resistors 96, 91 and 98. In this timing circuit the voltage change across resistors 91 and 98 is impressed between the grid and cathode of tube V8 while the condenser is charging. rIhe condenser is discharged quickly by relay 99 in the plate circuit of tube V8 at the end of the timing interval.

At the beginning of a timing operation positive voltage is impressed by the power supply on a circuit path comprising conductors 93 and |00, resistor |0| having a resistance value, say of 10,000 ohms, condenser 95 of a capacitance value of, say 0.5 microfarad, interconnected resistors 96, 91 and 98 having resistance values, say of 3600 ohms, 10 megohms and 50,000 ohms, respectively, to connection |02 on the grounded side of the power supply. This positive voltage is also applied through resistor |03 of a resistance value, say of 1 megohm, to the grid of tube V8 causing its grid to be effectively positive with respect to its cathode. Tube V8 conducts, the current owing through a path extending from the source of positive voltage at connection |04, conductor |05, through the winding of relay'99,con ductor |06, resistor |01 having a'resistance value, say of 33,000 ohms, conductor |08, plate and cathode of tube V3, conductor |09, to'a fixed potentiometer comprising resistorsV l0 and having resistance values, say of 5000 ohms and 17,000 ohms, respectively, the potentiometer having its source of supply from connections |04 and |02.

When condenser 95-becomes fully charged from the source of positive voltage at connectionl04, the positive potential at connection |20 decreases causing the grid of tube V8 to become negative with respect toits cathode. Therefore, tube V8 becomes non-conducting and causes relay 99 to release. Relay 99 upon releasing, provides (1) at its outer upper armature and back contact a path for discharging condenser 95, which discharges, 2) at its inner upper armature and back contact a path extending over` conductor I 2I for discharging the peak-distortion measuring condenser I8 in the transmission measuring set and condenser I8 discharges, and (3) at its lower` armature and back contact a path including condenser H2 and resistor H3, having one end connected to connection point H4 of positive polarity and the other, to connection point |92 of ground, or negative polarity to effectively delay conduction in tube V8 and consequently the operation of relay 99 for a denite short interval once the relay has released. The charging time of condenser H2 delays the conduction of tube V8 in order that condenser 95 may become fully discharged before tube V8 conducts again to reoperate relay 99. When relay 99 does reoperate at the time tube V8 begins conduction, the closure of the lower armature at its front contact closes a path for discharging condenser II2 and condenser H2 discharges.

The above operations are repeated to eiect the automatic discharge of peak-distortion measuring condenser I8 at deiinite intervals of, say 0.5 to 10 seconds, as desired.

External oscilloscope Terminals H', V' and C' in Fig. 2 may be provided to which one or more oscilloscopes of any desired size may be connected, from time to time, by means of switch H5 or other suitable means so that distortion may be observed at one or more locations by groups of people, as in connection with demonstrations. The H' terminal is arranged to receive the triangular-shaped sweep voltage which is normally applied to horizontal plate No. 8 of cathode-ray tube I6 by the cathode circuit of the right-hand triode of tube V6. The V terminal is arranged to receive the voltage pips which are normally applied to vertical plate No. 4 of tube I6 through condenser Il of one of the differentiating circuits. The C terminal is connected to the reference ground of the measuring set.

Adjustment of bias potentiometer The method of adjusting bias potentiometer 33 as described herein, improves the accuracy of the bias indication, especially when the measuring set is operated with rounded wave shapes as usually received at the end of a subscribers or customers loop circuit. This method is referred to herein as a static method in that it uses steady marking current owing through the input of the set. Since other controls employed in the set of the present invention can be set properly on regularly received signals, local checks with good, or test, signals are not required. This is a considerable advantage for a set adapted for portable use.

The input trigger-tube circuit which includes tube VI is designed to have operating characteristics similar to those of an electromagnetic relay in good electrical and mechanical condition.

The receiving relay of a measuring set such as disclosed in Patents 2,132,278 and 2,370,685, respectively, granted to F. A. Cowan and Rea et al., supra, is generally adjusted with 20-cycle ringing current having a sine wave shape. When properly adjusted the relay operates at nearly the mid-point of the Wave, that is, at nearly zerocurrent. The operating point obtained with this dynamic test is a little above the point of zero current in one direction and the releasing point is a little below zero current in the other direction. When a source of ringing current is not available, a static method of adjustment is used. In this case the relay is tilted in one direction and then in the opposite direction in order to cause the relay armature to fall to one contact and then to the other. 'I'he correct adjustment is obtained when the angle of tilt is the same in the two directions and of a given amount. The static method is reliable for relays in good mechanical condition.

When the input trigger-tube circuit including tube VI is properly adjusted for polar signals the left-hand triode conducts when the operating current rises a little above its zero value in one direction and becomes non-conducting when the current falls a little below its zero value in the other direction. One of these operating points may be determined by reducing the operating current to zero value, that is, operating key CP to its closed position to provide a shunt path across the input, and adjusting bias potentiometer 33 in one direction until the pulse-timer circuit just runs freely as indicated by the triangular-shaped sweep voltage-wave on cathode-ray tube it or on the external oscilloscope when one is provided as hereinbefore mentioned. The other of these operating points may be determined by adjusting bias potentiometer 33 until the triangular-shaped sweep voltage-wave just stops, with the shunt still connected across the input. The correct adjustment is midway between these two operating points. The correct operating point for neutral signals is about onehalf the value of the marking current. In order to determine these operating points for neutral signals the operating effect on the left-hand triode of tube VI is reduced to half value by connecting a shunt path across the input resistor 3| which has a resistance value, say of ohms, with resistor CN of the same resistance value, and this shunt path may be had by operating key CN to its closed position. Bias potentiometer 33 is then adjusted, iirst, in one direction and then in the opposite direction as hereinbefore described for polar signals. The correct setting of bias potentiometer 33 is then midway between the two operating points.

What is claimed is: l 1. A device for displaying along an axis of the screen of a cathode ray tube luminous manifestations to indicate and measure bias, end distortion and peak distortion of telegraph signals comprising a source of start-stop permutation code signals, a cathode ray tube, an input circuit for receiving signals from said source, a signal timer circuit operative in response to the start element of a signal applied to said input circuit to maintain itself in a fixed operated condition for a predetermined duration, a pulse timer circuit for timing the elements of a start-stop permutation code signal and means connected therewith responsive to the operation oi said signal timer circuit for producing for eachv of said signals from said source a uniform triangularshaped wave having cycles corresponding in number to the elements in a signal from said source, circuit means for impressing said triangularshaped wave voltages on the horizontal deflection plates of said cathode ray tube to produce a cathodic beamsweep traveling to and fro Vfor each cycle atwa uniform rate across an axis of apreciarse said tube, and a YVdifferer-itiatingfc'lrcfuitpathlrre sponsive vto 'a portion-`of fthe output I-`voltage f said input circuitv vfor fcausing'a' momentarywertical deiiect-ion-insaid` cathodic beam sweep ATto produce a momentary "pip" ofy light inAv conjunction with the sweep whereby any-idisplacement of lan incoming signal'transitionfromitsfcorrect' position is indicated.

l2. A device for 'displaying -alongf'an vaxisfof the screen 'of a cathode 'ray tube' luminous' maniiestations on one side only `of-a zero "deii'ection position on said airis, to indicateand-measure bias, 4end distortion andi'peak distortion of-telegraph signals comprising a sourcefof startestop permutation code'signals, fa cathode `ray tube,

an input circuit for receiving` signals from said source, a signal 'timer-circuit operativein respouse to Athe start element-of`a signal applied to saidinput circuit to maintain itselfinaxed operated conditionfor a predeterminedduration, a pulse timer circuit for timing'theelements of a signal and means connectedltherewith responsive to the operationwoi said signal'L timer circuit :for producing for y'each 'of saidsignals from said source a uniform triangular wave having cycles corresponding'in number to Ythe elements in any signal from saidsource,v circuit means Afor impressing said triangularshaped Wave voltage on the horizontall'deflectionf plates of said cathode'ray tubel-toiproducef-af'cathodic beam sweep traveling toiandf fro foraeach cycle at a uniform rate across lanaxiscf.` said-tube, a diiierentiating circuit f'includin'g zrectifying means and responsive tota .portionof the.A output voltage of said input circuit` for causing simultaneously with each' transition ofi asignal :incoming from said source fa"Sharp:lmomentaryiuni form increase of' vcltagelzinieitherfof:twodirections, switching' means fortselectingfthef :direc-V tion of voltage increase;.otherffcircuit meansrfor utilizing the-"increase in voltage in Aone :direction to intensify the" luminosity ofl'thefmani-festation to indicate lbias, and Vend 'distortion on the sweep along thel axis of their-screen `of said1 tube, .and va thirdcircuit'rneans' for vutilizing the increase in voltageA in theother :of said idirections to sample at thetime oi a transition-in the-.rincoming.'sig nal the-uniform ltriangular-sh'aped/-wave voltage, rectifying means lfor rectifying c:said sampled voltage, storing'means for storing the rectiied sampled voltage, a fourthcircuitffmeans. fori impressing the Voltage stored in4 saidstoring :means on the horizontal plates of said tube to produce a spot of'light in conjunctionwith ,the Ysweep along the axis of the screen of said tube whereby peak distortion is indicated.

3. A device for displaying along an axis of the screen offa cathode ray tube luminous man1- iestations on one side only Vof a zerovdeiiection position of said axis, to indicate and measure end distortion and peak distortion of telegraph signals Ycomprising a `source of start-stop permutation code signals, .acathode rayf-tubefan input circuit for receivingsignals from-said sourcer-a signal timer circuit operative in response. .tothe start element of a :signal applied to saidinput circuit to -maintain itself in aiixed. operated condition for `a predetermined duration, a .pulse timer circuit -forltiming the. elements of a signal and means connected therewith responsivev to the operation of said signal timer circuit for producing for each or" said signals from said source a uniform triangular-shapedwave having cyclescorresponding in number to the .elements 4in any signalfr'o'm' said source. circuit means for impressing said triangular-shaped wave voltageL on *the l'lcr-izontalvy deiiection 'fplates fof f-said cathode ray tube'toproduce va cathodic beam sweep travelingto and 'iro for each cycle-at 4a uniform rate acrossan axis of the screen of said tube, a dierentiating circuit including 'rectifying means and responsive to a portion of the output Voltage of said input. circuit for causing'simultaneously with each transition of asig nal incom-ing from-said source a sharp momentary uniform increase of Voltage in either of two 'directionsswitching means for Aselecting the direction 'of increase of voltage, other circuit meansffor utilizing the increase in Voltage in one direction to intensify the luminosity of the manifestation to indicate' bias and end distortion on the sweep along the axis of the face or said tube, and a third circuit means for utilizingthe increase 'in voltage in the other or" said directions to sampleat the time of atransition in the incoming signal the uniform triangular wave Voltage, rectifying means for rectifying said sampled voltage, storing means for storing the rectified sampled voltage, a fourth'circuit means for impressing the stored voltage on the horizontal plates of said tube to produce 'a spot of light-in conjunction with the sweep along the axis'of the screen of said tube whereby-peak distortion is indicated, and a fth circuit. means including a recording instrumentality for utilizing said storedvvoltage for producing a permanent record of Said stored voltage whereby a permanent record of the peak distortion Versus time,is obtained.

4. A1A device for displaying along an axis on the screen f a cathode ray tube .luminous manifestations ony one vside only of av zero deflection .position -of said axis to indicate andimeasure bias, end distortion and peak distortion of telegraph signals comprising a source of start-stop permutaticncode signalsga cathode ray tube, an input circuit for receiving signals from said source, a signal timer'A circuit operative inresponse to the start element of a signal applied to said input circuit to .maintain itself in a iiixed operated condition for a predeterminedfduration, a pulse timer circuitl for? timingl the elements of a signal and meanszconnected therewithfrespcnsive to the operation of said signal timer circuit for producing for eachof said-"signalsfrom` said source a uniform triangular-shaped wave having cycles cor- -responding in number to the elements in any signal from said.sourcecircuit means for impressing-said triangular.shaped Wave voltage on the .horizontal'deection plates .of said cathode ray tube toproduce a cathodic beamlsweep traveling .toand fro .for each .cycle at a uniform rate acrossanaxis of the screen of said. tube, a "differentiating circuit including. rectifying means and responsive to a portion` of the output Voltage of said ,input circuitv for causing simultaneously with each transition of a signal incoming from said source a sharp momentary uniform increase of'voltage inV either of two directions, switching means for selecting the direction `of increase. of voltage, other circuit meansv for utilizing the increase of voltage in one vdirection to intensify the luminosity of'thermarn'festation to indicate bias and'end' distortion on' thev sweep along the axis of said tube, andra third circuit meansY for utilizing' the increase in voltage in the other of saiddire'ctions to sample at the time of a transition inthe 'incoming signal the uniform triangular`shaped wave voltage, rectifying means for re'ctifying said lsampled voltage, Astoririgmeans for storing' the rectified sampled voltage, aA fourth circuit "means -for impressing the Voltage stored in said storing means on the horizontal plates of said tube to produce a spot of light in conjunction with the sweep along the axis of said tube whereby peak distortion is indicated, and resetting means including a timing device for automatically restoring said storing means to normal at regularly recurring intervals each of predetermined duration.

5. A device for displaying along an axis on the screen of a cathode ray tube luminous manifestations on one side only of a zero deflection position on said axis, to indicate and measure bias. end distortion and peak distortion of telegraph signals comprising a source of start-stop permutation code signals, a cathode ray tube, an electronic input circuit for receiving signals from said source and for reversing the sign of the elements of said signals, an electronic character timer circuit operative in response to the start element of a signal applied to said electronic d input circuit to maintain itself in an alternate stable condition for a predetermined duration, an electronic pulse timer circuit and an integrating circuit connected thereto responsive to the operation of said character timer circuit for producing for each of said signals from said source a uniform triangular-shaped wave having cycles corresponding in number to the elements in any signal from said source, circuit means for impressing the voltage of said triangular-shaped wave on the horizontal dellection plates of said cathode ray tube to produce a sweep traveling to and fro for each cycle at a uniform rate across the horizontal axis of the screen of said tube, a differentiating circuit including a condenser and a vertical plate of said cathode ray tube and responsive to a portion of the output voltage of said input circuit for causing a momentary vertical deflection in the cathodic beam to produce a short momentary vertical pip of light along the horizontal sweep whereby any displacement of an incoming signal transition from its correct position is indicated, another differentiating circuit responsive to another portion of the output voltage from said input circuit and including a condenser and a pair of rectiflers connected in parallel thereto, and circuit means for sampling the voltage of the uniform triangular wave at times of occurrence oi transitions in the signals from said source, other circuit means for storing said sampled voltages, and a third circuit means for impressing said stored voltages on the horizontal deflection plates of said tube to produce along the sweep across the horizontal axis of the screen of said tube a spot of light for indicating the amount or" peak distortion.

6. A device for displaying along an axis on the screen of a cathode ray tube luminous manifestations on one side only of the zero deilection position of said axis, to indicate and measure bias, end distortion and peak distortion of telegraph signals comprising a source or" start-stop permutation code signals, a cathode ray tube, an electronic input circuit for receiving signals from said source, an electronic signal timer circuit operative in response to the start element of a signal applied to said input circuit to maintain itself in a fixed operated condition for a predetermined duration, an electronic pulse timer circuit for timing the elements of a signal and means connected therewith responsive to the operation of said signal timer circuit for producing for each of said signals from said source a uniform triangular-shaped wave having cycles corresponding in number to the elements in the signal, circuit means for impressing said triangular-shaped wave voltages on the horizontal deilection plates of said cathode ray tube to produce a cathodic beam sweep traveling to and fro for each cycle at a uniform rate across the axis of the screen of said tube, a source of steady potential and a potentiometer connected thereto for biasing said electronic input circuit, a second source of steady potential for operating said electronic input *circuit, means for calibrating said device comprising means for closing a shunt path across said source of signals whereby current from said signal source is prevented from iiowing into said input circuit, and means manually operable during the time when signal source shunting means is closed for adjusting said potentiometer in one direction until said electronic pulse timer begins to operate freely with energy furnished by said source of steady potential, and then in the other direction until the said electronic pulse timer stops operating, whereby the mid-point between said point of beginning and said point of stopping is the desired calibrated position.

7. In a `device for displaying along an axis on the screen of a cathode ray tube luminous manifestations on one side only of a zero deflection position of said axis, to indicate and measure bias, end distortion and peak distortion of telegraph signals comprising a source of start-stop permutation code signals, a cathode ray tube, an electron discharge input circuit for receiving signais from said source, an electron discharge signal timer circuit operative in response to the start element of a signal applied to said input circuit to maintain itself in a fixed operated condition for a predetermined duration, an electron discharge pulse timer circuit for timing the elements of a signal and means connected therewith responsive to the operation of said signal timer circuit for producing for each of said signals from said source a uniform triangular-shaped wave having cycles corresponding in number to the elements in a signal from said source, circuit means for impressing said triangular-shaped wave voltages on the horizontal deflection plates of said cathode ray tube to produce a cathodic beam sweep traveling to and fro for each cycle at a uniform rate across the axis of the screen of said tube, a method of calibrating said device consisting in shunting signals away from the electron discharge input circuit, Varying in one direction the steady biasing potential normally applied to said electron discharge input circuit when said circuit is idle, until the instant when the input circuit starts operating to operate said electron discharge pulse timer circuit for a denite duration, varying in another direction the steady biasing potential until the instant when the input circuit stops operating whereby the electron discharge pulse timer circuit stops operating, and changing the steady biasing potential to a value midway between the instantaneous values whereat the operation of said input circuit starts and stops, respectively.

SAMUEL I. CORY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,107,149 Hearn Feb. 1, 1938 2,132,678 Cowan Oct. 11, 1938 2,480,878 Rea Sept. 6, 1949 2,481,354 Schuler Sept. 6, 1949 

